1. Field of the Invention
The present invention relates to a gear-shifting apparatus for a bicycle, and to a bicycle incorporating the apparatus. More particularly, the invention relates to a gear-shifting apparatus of a type using a chain, which shifts the chain from one sprocket to another.
2. Background
One example of a known gear-shifting apparatus for a bicycle is disclosed in Japanese Patent Laid-open Official Gazette No. 2004-155280. This known system includes a drive sprocket connected to a crankshaft through a one-directional clutch, while the drive sprocket is being driven. The known gear-shifting apparatus of this reference also includes a sprocket cluster constituted of a plurality of gear-shifting sprockets, which is connected to an output axle for driving a rear wheel, a chain hooked to the drive sprocket and one of the gear-shifting sprockets, a gear-shifting mechanism, and a case. The gear-shifting mechanism includes a derailer arm for rotatably supporting a guide pulley for guiding the chain to a selected gear-shifting sprocket. When the derailer arm moves along with the guide pulley in the center axis direction of the derailer axle, the chain is shifted from a current gear-shifting sprocket to the selected gear-shifting sprocket among the sprocket cluster. In this way, a gear-shifting operation is done. In addition, the case contains the drive sprocket, the sprocket cluster, the chain and the gear shifting mechanism.
Out of the plurality of gear shifting sprockets, the sprocket which is next to the case in the axis direction is referred to as an adjacent sprocket. If a quick gear shifting operation is performed for the purpose of changing the chain to the adjacent sprocket, the chain moves forcefully in the axis direction along with the guide pulley of the derailer. In such a case, in order to prevent the chain from moving in the axis direction beyond the adjacent sprocket due to inertia and coming off from the adjacent sprocket, a position in the axis direction of the chain or the guide pulley needs to be set with high precision, in response to a gear shifting position based on a gear shifting operation. However, it takes long time to set the position.
The present invention has been made against such a background. An object of the present invention is to provide a gear shifting system which does not require a position of the chain to be set with high precision in response to a gear shifting position, and which prevents the chain form coming off from the adjacent sprocket in conjunction with a quick gear shifting operation. A further object of the present invention is to additionally reduce costs for, and weight of, the gear shifting system provided with a configuration for preventing the chain from coming off the adjacent sprocket. A still further object of the present invention is to additionally improve prevention of chain derailment, and additionally make the case of the gear shifting system highly rigid.
A first aspect of the present invention includes a gear shifting system which comprises a plurality of gear shifting sprockets arranged in an axis direction, and a changing mechanism for changing a chain from one gear shifting sprocket to another among the plurality of gear shifting sprockets for the purpose of performing a gear shifting. The gear shifting system also includes a case in which the plurality of gear shifting sprockets and the chain are contained. In the case of the gear shifting system, a check part is provided for preventing the chain from moving in the axis direction so as to be too close to the case. When viewed from the side, the check part overlaps with a hooked part of the chain engaging with an adjacent sprocket, the adjacent sprocket being the closest sprocket to the case in the axis direction out of the plurality of gear shifting sprockets. The check part prevents the chain from coming off from the adjacent sprocket by means of contact of the check part with the chain.
The check part of the gear shifting system prevents the chain from moving in the axis direction beyond the adjacent sprocket while a gear shifting operation is changing the chain to the adjacent sprocket. Accordingly, the chain will not come off from the adjacent sprocket. For this reason, the position in the axis direction of the chain is not required to be set with high precision, in response to a gear shifting position based on a gear shifting operation.
A second aspect of the present invention includes the invention described above, and further includes the check part being constituted of a protruding part which is molded integrally with the case in a way that the protruding part protrudes towards the hooked part in the axis direction.
In the case of this gear shifting system, since the protruding part constituting the check part is molded integrally with the case, it is not necessary to prepare a specialized member for constituting the protruding part.
A third aspect of the present invention includes the invention described above, and further includes providing the case with a reinforcement rib. The rib extends from the protruding part outwards in a radial direction of the adjacent sprocket, in a way that the reinforcement rib protrudes in the axis direction. A top surface in the axis direction of the reinforcement rib is located in almost the same position as the check part which checks the chain from moving in the axis direction by means of contact of the check part with the chain in the protruding part.
In the case of this gear shifting system, rigidity of the case is further increased by means of the reinforcement rib. In addition, even in a case where a part of the chain extends outwards in the radial direction beyond the protruding part, the part of the chain which extends outwards is prevented from moving in the axis direction beyond the protruding part.
According to the first aspect of the invention, while a gear shifting operation is changing the chain to the adjacent sprocket, the check part prevents the chain from coming off from the adjacent sprocket. For this reason, a position of the chain is not required to be set with high precision in response to the gear shifting position. Accordingly, by means of a simple configuration, the chain is prevented from coming off from the adjacent sprocket due to a quick gear shifting operation.
According to the second aspect of the invention, a specialized member for constituting the protruding part is not required. Accordingly, the number of the parts of, and costs for the gear shifting system are reduced. In addition, the resulting gear shifting system is lighter in weight.
According to the third aspect of the invention, the rigidity of the case of the gear shifting system is increased by means of the reinforcement rib. In addition to the check part, the reinforcement rib prevents the chain from coming off from the adjacent sprocket. Accordingly, the effect of preventing the derailment of the chain is further improved.
Modes for carrying out the present invention are explained below by reference to an embodiment of the present invention shown in the attached drawings. The above-mentioned object, other objects, characteristics and advantages of the present invention will become apparent form the detailed description of the embodiment of the invention presented below in conjunction with the attached drawings.